This invention relates to high performance chromatography to provide high performance chemical separations and purifications by reverse phase chromatography.
High performance liquid chromatography today means separations processes for performing liquid chromatography at higher speeds and separation powers not available in classical liquid chromatography. Separation processes are performed in minutes instead of hours or days, and some new column packings provide separations that were previously impossible.
Reverse phase chromatography processes involve adsorption on an adsorbent less polar than the eluting solvent. Contrastingly, normal phase chromatography processes involve an adsorbent more polar than the eluting solvent. In reverse phase chromatography separation processes, the more non-polar sample components interact more with the relatively non-polar column packing and thus elute later than polar sample components.
U.S. Pat. No. 4,045,353 discloses prior art processes for high speed liquid chromatography using an organic compound or organic polymer gel on an inorganic substrate. Suitable polymerizable monomers include the ethylenically unsaturated monomers, e.g., such as styrene monomer, fluorine monomer, silicon-containing monomer, acrylates, methacrylates, vinyl monomer, olefin monomers, diene monomers, e.g., such as butadiene, isoprene, 1,3-pentadiene, cyclopentadiene, chloroprene, or other monomers capable of being radiation polymerized such as the aldehydes, ketones, cyclic ethers, or the like. Such a polymer can be grafted (the patent discloses) on a substrate of "silica, silica gel, alumina, diatomaceous earth, zeolite, porous glass, carbon black, active carbon, clay, etc."
Many processes for high performance liquid chromatography use silica-based reverse phase packings but these materials have problems associated with a relatively narrow operating pH range, e.g., such as about 2-8, and a high pressure drop requirement. The narrow operating pH range of silica materials usually results in a shorter column life, a loss of separations versatility, and difficulty in the cleanup with strong alkali and acid for cost effective, high speed analytical, semi-preparative and preparative purification of samples. The high pressure drop of the silica-based materials also limits the ultimate speed and separation capabilities of the chromatography column.
Aluminas have been used frequently in classical adsorption chromatography, but the use of aluminas as media for modern high performance liquid chromatography in the reverse phase has been less than silica because alumina is not easily converted to a hydrophobic phase for selective chromatographic separation via chemical bonding the surface by various hydrocarbon groups, e.g., alkyl or phenyl. The prior art has found that most silanization reagents used successfully with silica show no reactivity toward aluminas. Although chlorosilanes react with alumina, the formed Al--O--Si--C bond is known to be highly unstable under reverse phase chromatographic conditions.
It is an object of the present invention to provide a process for performing reverse phase chromatography.
It is another object of the present invention to provide a process for performing reverse phase chromatography at a lower pressure drop through the separations column.
It is a further object of the present invention to provide a process for performing reverse phase chromatography at a wid range of pH.
It is yet another object of the present invention to provide a process for performing reverse phase chromatography to separate and purify basic, nitrogen-containing compounds.
These and other objects of the present invention will become apparent from the detailed description which follows.